The Significance Of Clay Minerals Characteristics & The Environmental Changes In Lower Reaches Of The Yangtze River

Clay minerals are distributed in different types of deposits and sedimentary rocks. As secondary minerals they are highly sensitive to environmental changes. The characteristics of clay mineral such as sedimentary differentiation, composition and assemblage, crystallinity and stable isotope have recorder the information of environmental change during the processes of clay minerals formation.This article selects Chaohu Lake basin and Chenghu Lake of Taihu Lake basin in Lower Reaches of the Yangtze River as the study area. So we attempted to study the past environmental evolution from the samples which including surface soil of Hangbu River catchment, ALE ,AC4,AC5 and CH core of Chaohu Lake catcgment,SC6 and SC7 core of Chenghu Lake et al. A large number of date have been obtained by systematical measure of clay mineral,content of grain size and ²¹⁰Pb dating to calculate sediment of CH core. By statistical analysis of these date from the sediments we discussed the clay mineral composition, formulation, crystal texture and distribution characters which had been influenced by the environment of the catchments.1,The dominate clay mineral of recent sedimentation in Chaohu Lake are illite (53.69-64.51%) ,kaolinite(17.9-23.18%), vermiculite(8.27-14.2%), chlorite (4.37 -5.58%) and smectite(2.86-3.39%),The clay minerals composition character is Illite-kaolinite-vermiculite-chlorite-smectite, Illite's Kübler index is 0.4, illite crytsallinity is very low,which are strongly-weathering products;The clay mineral in hard clay are also the five mineral, the minerals quantity are 73.58%, 14.74%, 4.15%, 4.52% and 3.01%.The composition character is Illite-kaolinite-vermiculite+chlorite +smectite, illite's Kübler index is 0.23, illite crytsallinity is high,which all showed that the clay minerals had undergone a stronger weathering than recent.2,The dominate clay minerals of recent sedimentation of Chenghu are illite (70.77%),chlorite(12.64%),kaolinite(10.74%),smectite(4.25%),vermiculite(1.6%),the minerals composition characters are all illite-chlorite+kaolinite-vermiculite +smectite, Illite's Kübler index are 0.22, illite crytsallinity are high,which showed a weakly-weathering environment; In the hard clay band, the dominate clay minerals are illite(52.3%), kaolinite(21.97%), vermiculite(12.35%), chlorite(10.68%) , smectite (4.25%), the minerals composition characters are illite-kaolinite-chlorite+ vermiculite-smectite, Illite's Kübler index are 0.19. Througe comparing with Chinese loess's, Illite and semctite quantity in the hard clay band under Chenghu Lake bed were lower than Chinese loess's, but kaolinite and vermiculite quantity wes higher than Chinese loess's, which reflected this hard clay band had experienced a strong eluviation and hydrolyzation.3,The formation of clay minerals in Lower Reaches of the Yangtze River had been influenced by the climate, geologic environment et al. The clay minerals composition character is Illite-kaolinite-chlorite-vermiculite-smectite.There were large of area igneous rock, bedrock et al, In mountain district in the Lower Reaches of the Yangtze River, the rocks of the Geologic are very complex. There are many micas in the weathering rocks fragments, those micas are effloresced to number of illite, So illite quantity is among the 53.66-70.77%.The climate of this area is humid and warm, the eluviation and hydrolyzation are very strong, the clay minerals are in the dissilicon and diskalium phase, soils are rich in kaolinite,the quantity is among the 10.74-20.92% in the sediments, which is higher than Huanghe River's 10% and at the same time lower than south of China's 20%.This area, chemistral weathering is dominant, the Na⁺, Ca⁺ are deprived from the smectite's crystalline layer. So the semectite quantity is only 2.86-4.25%.Chlorite is the sedentary production of the incipient weathering stage. In the upper reaches of Hangbu River, the chlorite high quantity is 23.9%, which is the soil lowerly-development symbol.4,The clay minerals distribution has intimate relationship with hydrodynamics and crystalline structure. In the river estuary area, the hydrodynamics is more intensity, the kaolinite and vermiculite quantity are higher, the illite and semectite quantity are lower; but in the center area of the lake, the hydrodynamics is poorer, the kaolinite and vermiculite quantity are lower, Illite and semectite quantity are higher. In the river estuary area, the water salinity is high and flocculating agent is strong, kaolinite(about 0.2nm) and vermiculite's crystal grain are coarse ,so they deposit easily. Illite(about 0.1nm) and semectite(about 0.01nm)'s crystal grain are very fine , they can be suspended in the water for long time, so they can be transported to the center lake where is far away from the river estuary.5, In the CH core, from the botton to top, smectite quantity is very low and decreased, but kaolinite quantity, K/S(kaolinite quantity / smectite quantity )ratio and illite's Kiibler index are increasd. Those characteristics had reflected that the Chaohu Lake's climate was gradually warm and humid. Especially, at the 60-25cm phase, Curve of the K/S ratio appeared a lower segments, which reflect that Chaohu Lake was in the usual discharged period ,At this period Chaohu basin wes lack of rain and the eluviation weakened.